Production of alkali-soluble cellulosic textile materials by the aluminum nitrate treatment of partially etherified cottons and the oxidation of cellulose with aluminum nitrate



United States Patent PRODUCTION 0F ALKALI-SULUBLE CELLULOSIC TEXTILE MATERIALS BY THE ALUMINUM NI- TRATE TREATMENT OF PARTIALLY ETHERI- FIED (IOTTONS AND THE OXIDATION OF CEL- LULOSE WITH ALUMINUM NITRATE Robert M. Reinhardt, New Orleans, and Russell M. H-

Kullman, Metairie, La., assignors to the United States of America as represented by the Secretary of Agriculture No Drawing. Filed Feb. 17, 1965, Ser. No. 433,523

8 Claims. (Cl. 8-120) A non-exclusive, irrevocable, royalty-free license in the invention herein described, throughout the world for all purposes of the United States Government, with the power to grant sublicenses for such purposes is hereby granted to the Government of the United States of America.

This invention relates to an improved process for producing alkali-soluble cellulosic textile materials. More specifically, it relates to a process wherein the cellulose is mildly etherified and then treated with an oxidationagent precursor. Upon exposing the treated cellulosic textile material to dry heat, the precursor is decomposed, the oxidant is liberated and, simultaneously, the partially etherified material is oxidized. The resulting chemicallymodified cellulosic textile material may be processed on conventional textile machinery, has a high degree of solubility in alkaline solutions, and upon dissolution leaves little or no insoluble residue. These alkali-soluble products have many commercial uses.

As used herein, the term cellulosic textile materials relates to the natural (native) and synthetic celluloses in the form of yarns, fabrics, knitted products, and webbing. Because of its wide use in the industry, cotton will be frequently used below for illustrative purposes.

The expression partially etherified cellulose, as used herein, relates to cellulosic textile materials which have been mildly etherified to have a degree of substitution (DS) ranging from about 0.04 to 0.40. These will be discussed more fully below.

The term oxidation agent precursor, as used herein, relates to metal nitrates, particularly aluminum nitrate, which readily decompose upon exposure to dry heat, libcrating oxides of nitrogen, and (nascent) oxygen.

Etherification of cotton to a low degree of substitution (D) of the order of 0.04 to 0.40 is readily accomplished. The classical chemistry of native cellulose modification is also operative in the reactions of partially etherified cotton, except the rate and extent of subsequent treatments are sometimes much greater with the etherified cottons than with the native (unmodified) cotton. Because of this greater activity, partially etherified cottons can be treated with many oxidizing agents under much milder conditions than with native cotton. The practical result of these mild reaction conditions is that the alkalisoluble cottons can be produced with greater retention of the useful textile properties of the cotton fiber.

In U.S. Patent 3,052,511, there is disclosed a process for the production of alkali-soluble cotton textile materials by employing an exceedingly mild chemical modification of the original (native) textile material followed by an oxidizing treatment using nitrogen dioxide, either in the gaseous or liquid phase, in solution in an inert organic solvent, or generated in situ from aqueous solutions of nitrite salts and aqueous acids. In the process of this patent, the term nitrogen dioxide designates the equilibrium mixture of nitrogen dioxide (N0 and dinitrogen tetroxide (N 0 which normally exist under the various conditions of use. The resultant chemically modified and subsequently oxidized material has excellent alkali solubility.

Patented Mar. 12, 1968 However, the use of nitrogen dioxide in any of the above forms has several disadvantages. In the first place, nitrogen dioxide is a toxic gas and must be confined. As a result, treatment of the textile material may require a batch operation or the apparatus must be equipped with a vapor lock. This type of equipment is expensive. Further, nitrogen dioxide is very corrosive and damaging to the expensive machinery. In the second place, the equilibrium mixture NO =N O which is a liquid occurs at about 21 C., and at this temperature the liquid N 0 could be maintained only by means of external cooling. In the third place, the use of a solution of the equilibrium mixture in an inert solvent is accompanied by a fire and/or an explosion hazard as well as the added expense of the inert solvent which must subsequently be removed by further Washing. In the fourth place, generating the nitrogen dioxide or dinitrogen tetroxide in situ requires high concentrations of phosphoric acid of the order of about 70-80%. Finally, the required oxidizing times ranging from about 0.5 to 2.0 hours to obtain good alkali solubility are too long for a continuous operation.

Therefore, prior to this invention there still remained a need for an improved, commercial. process employing the oxides of nitrogen for the oxidation of partially etherified cellulosic textile materials to produce satisfactory, alkali-soluble products having excellent retention of the original fiber properties. Such a process should be economical. It should be simple and easily carried out in presently-available commercial equipment. Last, but not least important, it should be free of toxic fumes and the hazard of fire and/ or explosion.

In general, the overall process of the present invention may be simply described. The unmodified cellulosic textile material is subjected to the following operations. Therein, all proportions and percentages are based on the weight of the fibrous material (owf) or upon the weight of the solution (ows) unless otherwise noted. Temperatures are in degrees centigrade.

(l) The cellulosic textile materials are partially etherified by conventional procedures to a low degree of substitution of from about 0.04 to 0.40 ether groups per anhydroglucose unit. Ether groups selected from the group carboxyethyl, carboxymethyl, hydroxyethyl, methyl, and phosphonomethyl are preferred although other etherified cottons may be used including ethyl, u-methylcarboxymethyl, aminoethyl, carbamoylethyl, sulfoethyl, and the like. The preferred chemical modification for the process of this invention is partial etherification applied as described in the specific examples that follow. Regardless of the chemical modification treatment employed, the advantageous feature of the process of this invention is that the chemical modification need not be carried beyond a degree of substitution of about 0.4. Aside from the consideration of retaining the textile properties of the chemically-modified material, the possibility of operating at a low degree of substitution possesses obvious economic advantages.

(2) The partially etherified cellulosic material is then impregnated with a solution of aluminum nitrate by passing the material into, and through, said solution. Concentrations of this solution may range from about one weight percent (ows) to a saturated solution. The preferred aluminum nitrate is the nonahydrate (Al(NO -9H O). It is readily soluble in aqueous solutions, melts in its water of crystallization at 73 C. to form Al(NO -5H O, and decomposes at about C. to give the metal oxide, nitrogen dioxide, and oxygen. The overall decomposition reaction can probably be represented by the following formula:

During the reaction, the oxygen is first liberated as nascent oxygen and is an excellent oxidizing agent. Further, at a temperature of about 140 C., the nitrogen dioxide also decomposes liberating additional oxygen according to the following:

140 plus Aluminum nitrate has found commercial use in the electrical industry, in petroleum refining, and in leather tanning. In the textile industry, aluminum nitrate has been used as a mordant for textile printing and for lake dyes. No use of aluminum nitrate has been made for the oxidation of cellulosic textile materials.

Other nitrates of the less-positive metals also may be employed as oxidation-agent precursors in the process of this invention.

(3) The aluminum nitrate-impregnated material is then passed through pad rolls, or squeeze-rolls, to remove the excess solution and to give a wet pickup of about 100 weight percent on the weight of the dry cellulosic material, This process may be carried out in conventional tex' tile-processing equipment as the aqueous solution of aluminum nitrate is only Weakly acidic.

(4) The impregnated material is then heat-treated using conventional textile processing procedures and equipment. During this treatment, the fabric is first dried, the oxidation-agent precursor is melted and subsequently decomposed to give oxides of nitrogen and oxygen as discussed above. Simultaneously, the partially etherified cellulosic material is oxidized.

The temperature of the heat treatment may vary from about 120 to about 160 C. and the time may vary from about five minutes to one minute, the shorter time being at the higher temperature. Thus the time and temperature of the treatments are inversely related.

It is also within the scope of this invention to dry the cellulosic material impregnated with the oxidation-agent precursor at a lower temperature (below about 110 C.) and subsequently heat treat at the higher temperatures to decompose the oxidation-agent precursor and bring about oxidation. This embodiment permits holding the treated but unoxidized cellulosic material for an indefinite period prior to oxidizing the partially etherified cellulose and is of considerable value in programming the workload. Most important, low-temperature dried materials retain all of the strength of the etherified material.

It is an advantage of the process of this invention that control of the concentration of the oxidation-agent precursor is much easier than the use of gaseous oxides of nitrogen. It is a further advantage that the process does not require special equipment for application of the oxides of nitrogen to the partially-etherified cellulosic textile material. It is a still further advantage that the process is readily carried out in a batch oven, or by a continuous process in which a tenter frame, steam cans, or a hightemperature loop drier may be used.

It is a still further advantage of our invention that selective solubilization of one member of a product is possible. For example, if one ply of a multi-ply yarn (two or more plies) is partially etherified and treated with aluminum nitrate prior to spinning, subsequent heat treatment of the two-ply yarn will permit dissolution of the partiallyetherified and aluminum nitrate treated ply with sodium hydroxide solution.

By adjustment of the degree of substitution obtained in the etherification step, the concentration of aluminum nitrate (or other oxidation-agent precursor) applied, and the time and temperature employed in the heat treatment, cellulosic products of a wide range of alkali-solubility, up to and including complete solubility, may be prepared by the process of this invention.

It is known that mild oxidation of cellulose with nitrogen dioxide yields an oxycellulose which is partially soluble in alkali, whereas more rigorous oxidation brings about complete solubility but with considerable degradation. The principal oxidation reaction is the formation of uronic acid units. Other oxidation reactions also occur which produce, in addition to the carboxyl groups of the uronic acid units, aldehyde groups, carbonyl groups, and nonuronic acid carboxyl groups. These groups also contribute to the alkali solubility of the products.

Partially etherified cottons offer two principal theoretical advantages over untreated cotton for the production of alkalisoluble derivatives by oxidation. These advantages are: (1) Presence of solubilizing groups which enhance alkali-solubility through greater solubility of alkali- =cleaved fragments. (2) Opening up of the crystalline regions of the fiber for more uniform and increased reaction. These properties are achieved by variations in the methods of preparation and chemical nature of the substituent group introduced.

Many etherified cottons bear a substituent group which in itself confers solubility upon the derivative. Oxidation of unsubstituted 6-alcohol groups to carboxyl groups introduces another solubilizing group. Oxidation of unsubstituted 2,3 glycol units causes alkali-lability. The combined effects added together result in high solubility from relative low degree of reaction. A small amount of oxidation causing a limited amount of cleavage in alkali can be very effective if the cleaved fragments hear an alkalisolubilizing group. Thus, fragments of longer chain length than are usually soluble will go into solution.

Therefore, the alkali-solubility of oxidized, partiallyetherified cotton theoretically combines disintegration with true macro-molecular solution.

The preservation of the original textile properties in an alkali-soluble textile material is most valuable and highly desirable since, even though for many uses the presence of the alkali-soluble material is transient, it is essential that the alkali-soluble product, while it exists in textile form, be capable of being processed on conventional textile machines. The obvious requisites are, of course, retention of strength, flexibility, and abrasion resistance. A typical use for an alkali-soluble textile material is as a scaffolding or supporting foundation for the preparation of light, or novelty yarns and fabrics. By alternating soluble textile yarns with nonsoluble textile yarns, in weaving and then subjecting the woven product to dissolution, open-work fabrics and other novelty effects may be achieved. Knit socks may be produced in a continuous string, each connected to its neighbors by a thread of soluble yarn. The socks after fabrication may then be readily separated by simple disintegration of the soluble connecting yarns. Soluble textile materials are also used as backing in the manufacture of lace. In the medical field, soluble textile materials have found application as bandages, compresses, and sutures.

Having thus described in a general way the operation of the process of this invention, details of the process are listed below in specific examples which describe the application of the process to textile materials.

The following examples are presented to illustrate in greater detail certain features involved in the practice of the present invention. However, it is apparent that many modifications can suitably be made. The scope of the invention is defined by the claims and is not to be construed as being limited to the particular materials and conditions employed in the examples.

Example 1 A portion of scoured, unmercerized cotton printcloth was carboxymethylated to a D5 of 0.06 by treatment with chloroacetic acid and sodium hydroxide by the process of Daul and coworkers as disclosed in the Textile Research Journal, 22, 787-792 (1952). Swatches of this carboxymethylated cotton fabric were impregnated with aqueous solutions of aluminum nitrate nonahydrate of Alkali-Solubility l of Carboxy- Cone. of Aluminum Treat- Nitrate Solution ment methylated Cotton Treated for Used (Percent Temp., A1(NO .9H O) Deg. C. 1 Min. 2 Min. 3 Min. 5 Mm.

Solubility of treated fabric in boiling 10% aqueous sodium hydroxide solution, liquor to fabnc ratio 100:1. Results are shown as: S=Soluble; PS=Partially Soluble and I=Insoluble.

Similar treatment of scoured, unmercerized, unmodified cotton fabric using 25% aluminum nitrate nonahydrate with heat treatment at 140 for five minutes yielded a product which was insoluble in boiling 10% aqueous sodium hydroxide.

Example 2 Samples of scoured, unmercerized cotton printcloth were separately processed as follows: (a) carboxyethyl ated to degrees of substitution of 0.04 and 0.07 by treatment with aqueous solutions of acrylamide and sodium hydroxide by the process of Vaughan as disclosed in US. Patent 2,618,633, issued Nov. 18, 1952; (b) hydroxyethylated to degrees of substitution of 0.11 and 0.21 by treatment with ethylene oxide and sodium hydroxide by the process of Lawrie and coworkers as disclosed in the Journal of the Society of Dyers and Colouri-sts, 56, 6-17 (1940); (c) methylated to degrees of substitution of 0.09 and 0.34 by treatment with dimethyl sulfate and sodium hydroxide by the process of Reeves and coworkers as disclosed in Textile Research Journal, 25, 257-261 (1955); and (d) phosphon-ornethylated to degrees of substitution of 0.04 and 0.09 by treatment with chloromethylphosphonic acid and sodium hydroxide by the process of Drake and coworkers as disclosed in Textile Research Journal, 29, 270-275 (1959). A swatch of each was impregnated with aqueous 25% aluminum nitrate nonahydrate solution, by passing the treated fabric into, and through, the solution, then passing it through squeeze rolls to give 100% wet pickup, heated in an oven at 140 C. for five minutes, washed, and dried. The solubility of a portion of each treated swatch was determined in boiling 10% aqueous sodium hydroxide. Solubiiities are shown in Table II.

TABLE II Fabric treated: Alkali-solubility Carboxyethylated cotton, DS 0.04 PS Carboxyethylated cotton, DS 0.07 S Hydroxyethylated cotton, DS 0.11 PS Hydroxyethylated cotton, DS 0.21 S Methylated cotton, DS 0.09 I Methylated cotton, DS 0.34- S Phosphonomethylated cotton, B8 0.04 I Phosphonomethylated cotton, D8 009 S Example 3 A. A sample of scoured and mercerized cotton printcloth was carboxymethylated to a DS of 0.06 as in Example 1. It was impregnated with an aqueous solution containing 25% aluminum nitrate nonahydrate by passing the fabric into, and through, the solution and then passing the wet fabric through squeeze rolls to give a wet pickup of about 100%. The impregnated fabric 6 was then dried at 60 C. and divided into several portions. After the drying step, the fabric retained essentially all of the strength of the carboxymethylated material and was not soluble in boiling 10% aqueous so dium hydroxide solution.

B. One portion of the dried fabric was immediately heat-treated for three minutes at 160 C. This sample was completely soluble in boiling 10% aqueous sodium hydroxide solution and no gummy, sticky residue was observed.

C. One week after drying the aluminum nitrate-im pregnated partially carboxymethylated cotton (A above), the fabric was still insoluble in boiling 10% aqueous sodium hydroxide solution.

D. A portion of the fabric A was heat treated one Week after drying, as in B, to yield a product soluble in boiling 10% aqueous sodium hydroxide solution.

This example illustrates: (a) that fabric may be dried at low temperature and held for a period of time prior to heat-treating without adversely affecting the subsequent decomposition of the oxidizing agent precusor; (b) that an alkali-soluble textile material can be prepared by low temperature drying and subsequent (even after a considerable delay) heat-treatment of aluminum nitrateimpregnated partially etherified cotton; and (c) that alkali-solubility does not result until after heat treatment at a temperature sufficient to decompose the aluminum nitrate.

Example 4 A swatch of scoured and mercerized cotton printcloth was impregnated to Wet pickup with a 20% aqueous solution of aluminum nitrate non-ahydrate, and heated at C. for three minutes. This material was not soluble in hot 10% aqueous sodium hydroxide. The carboxyl content of a portion of the sample was determined. It was 1.02%, indicating oxidation of approximately 3.7% of the anhydroglucose units. The presence of carbonyl groups also was indicated by qualitative evidence.

A swatch of carboxymethylated cotton was oxidized using the same treatment conditions. C-arboxyl content of the etherified cotton before oxidation was 1.64% which corresponds to a degree of substitution. of about six carboxymethyl groups per 100 anhydroglucose units. After oxidation, the carboxyl content was 2.32%, and the material was readily soluble in hot 10% aqueous sodium hydroxide. After oxidation, carboxyl content was 0.68% higher than before. This may indicate that there was 1.64% COOH due to etherification and an increase of 0.68% COOH due to oxidation. Another possibility is that the oxidation-carboxyl content is higher, approximating the 1.02% of the oxidized-memorized cotton, with some loss of carboxymethyl groups due to cleavage of some of the ether substituent from the cotton in the oxidation treatment. In either case, it can be seen readily that oxidation does occur, and that the combination of etherification and oxidation by aluminum nitrate treatment is most effective in producing alkali-soluble products at lower degrees of oxidation than are sufiicient to produce alkali-solubility when unmodified cellulosic textiles are used as starting materials.

We claim:

1. A process for producing an alkali-soluble cellulosic textile that substantially retains its textile properties which comprises partially etherifying cotton textile to a degree of substitution of from about 0.04 to about 0.40 ether groups per anhydroglucose unit, said ether group being a member selected from the group consisting of carboxyethyl, carboxymethyl, hydroxyethyl, methyl, phosphonomethyl, ethyl, alpha-methylcarboxymethyl, aminoethyl, carbarnoylethyl and sulfoethyl, and oxidizing said partially etherified cotton textile by impregnating it to about 100% pickup with an aqueous solution of aluminum nitrate having a concentration from about one weight percent to a saturated solution, and dry heat treating the aluminum nitrate impregnated partially etherified cotton textile at a temperature of from about 120 to about 160 C. for from about one to about five minutes, the time and temperature of the heat treatment being inversely related, to dry said etherified cotton textile and decompose the aluminum nitrate.

2. The process of claim 1 wherein the partial etherification employed is carboxyethylation.

3. The process of claim 1 wherein the partial etherification employed is carboxymethylation.

4. The process of claim 1 wherein the partial etherificationemployed is hydroxyethylation.

5. The process of claim 1 wherein the partial etherification employed is methylation.

6. The process of claim 1 wherein the partial etherification employed is phosphonomethylation.

'7. A process according to claim 1 wherein the aluminum nitrate solution impregnated, partially-etherifiecl cotton is dried at a temperature below the decomposition point of the aluminum nitrate and subsequently heattreated at the temperature ranging from about 120 to 160 C. to oxidize the partially-etherified cotton.

8. A process for the oxidation of cellulose which com prises impregnating the cellulose to about 100% pickup with an aqueous solution consisting essentially of aluminum nitrate having a concentration from about one weight percent to a saturated solution, and dry heat treating the aluminum nitrate impregnated cellulose at a temperature of from about to about C. for from about one to about five minutes, the time and temperature of the heat treatment being inversely related, to dry said cellulose and decompose the aluminum nitrate.

References Cited OTHER REFERENCES Chemical Abstracts, vol. 43, Mar. 10, 1949, 1978i (author: Junji Torii).

NORMAN G. TORCHIN, Primary Examiner.

H. WOLMAN, Assistant Examiner. 

1. A PROCESS FOR PRODUCING AN ALKALI-SOLUBLE CELLULOSIC TEXTILE THAT SUBSTANTIALLY RETAINS ITS TEXTILE PROPERTIES WHICH COMPRISES PARTIALLY ETHERIFYING COTTON TEXTILE TO A DEGREE OF SUBSTITUTION OF FROM ABOUT 0.04 TO ABOUT 0.40 ETHER GROUPS PER ANHYDROGLUCOSE UNIT, SAID ETHER GROUP BEING A MEMBER SELECTED FROM THE GROUP CONSISTING OF CARBOXYETHYL, CARBOXYMETHYL, HYDROXYETHYL, METHYL, PHOSPHONOMETHYL, ETHYL, ALPHA-METHYLCARBOXYMETHYL, AMINOETHYL, CARBAMOYLETHYL AND SULFOETHYL, AND OXIDIZING SAID PARTIALLY ETHERIFIED COTTON TEXTILE BY IMPREGNATING IT TO ABOUT 100% PICKUP WITH AN AQUEOUS SOLUTION OF ALUMINUM NITRATE HAVING A CONCENTRATION FROM ABOUT ONE WEIGHT PERCENT TO A SATURATED SOLUTION, AND DRY HEAT TREATING THE ALUMINUM NITRATE IMPREGNATED PARTIALLY ETHERIFIED COTTON TEXTILE AT A TEMPERATURE OF FROM ABOUT 120* TO ABOUT 160*C. FOR FROM ABOUT ONE TO ABOUT FIVE MINUTES, THE TIME AND TEMPERATURE OF THE HEAT TREATMENT BEING INVERSELY RELATED, TO DRY SAID ETHERIFIED COTTON TEXTILE AND DECOMPOSE THE ALUMINUM NITRATE.
 8. A PROCESS FOR THE OXIDATION OF CELLULOSE WHICH COMPRISES IMPREGNATING THE CELLULOSE TO ABOUT 100% PICKUP WITH AN AQUEOUS SOLUTION CONSISTING ESSENTIALLY OF ALUMINUM NITRATE HAVING A CONCENTRATION FROM ABOUT ONE WEIGHT PERCENT TO A SATURATED SOLUTION, AND DRY HEAT TREATING THE ALUMINUM NITRATE IMPREGNATED CELLULOSE AT A TEMPERATURE OF FROM ABOUT 120* TO ABOUT 160*C. FOR FROM ABOUT ONE TO ABOUT FIVE MINUTES, THE TIME AND TEMPERATURE OF THE HEAT TREATMENT BEING INVERSELY RELATED, TO DRY SAID CELLULOSE AND DECOMPOSE THE ALUMINUM NITRATE. 